DESCRIPTION: Although the incidence of severe erythroblastosis fetalis is < 1%, due especially to the widespread use of Rh Immune Globulin, the outcome of this immunologic disorder is so severe that an algorithm calling for invasive procedures such as serial amniocentesis and percutaneous umbilical cord blood sampling has been adopted for use in all multigravida Rh negative pregnancies by the American College of Obstetrics and Gynecology. Rh negative women carrying Rh negative fetuses are not at risk for hemolytic disease of the newborn (HDN), but this cannot be determined without invasive procedures which carry not only expense and discomfort, but a finite risk of loss of the pregnancy as well. The investigators have developed a prototype assay for the identification of fetal blood group alleles using a DNA based method, using vertical gels that discriminate the major Rh alleles in a simultaneous array. This proposal intends to develop a kit for clinical use using this prototype method. The first kit iteration will be a manual one, using silver or fluorescent staining. Adaptation of the kit to use in conjunction with fragment analysis packages available with automated sequencers and small hand-held scanning devices will follow.